1. Field of the Invention
This invention relates to a method of bonding polysulfide sealant to a cured silicone elastomer.
2. Background Information
Both silicone sealants and polysulfide sealants are used on aircraft. In some instances, it is desirable to obtain a good bond between them when one is placed over the other.
Polysulfide compositions and their cure are taught in U.S. Pat. No. 2,964,503, issued Dec. 13, 1960. The polyalkylene polysulfide polymers can exist in solvent free, flowable liquid polymer form, which polymers are cured with a soluble salt of chromic acid. This patent teaches addition of a modifying and solubilizing agent selected from a stated group of liquids having a melting point below about 20.degree. C. and a boiling point above about 125.degree. C.
Curable liquid polyfunctional polysulfide polymer having reactive mercaptan groups are combined with an organic-silane and a curing agent to make a sealant composition is U.S. Pat. No. 3,123,495, issued Mar. 3, 1964. The silane is intended to aid in the resistance of the bond of the sealant to substrate to the detrimental effects of ultraviolet light. The organic-silanes are those having one or more alkoxy, aryloxy, acyloxy, amino, or vinyl groups in them. Especially useful are silanes having a vinyl or amine group and one or more alkoxy groups.
The use of beta-mercapto alkyl amino alkyl trialkoxy silanes as primers or additives for polysulfide polymer based sealants and caulking compounds is taught in U.S. Pat. No. 3,297,473, issued Jan. 10, 1967. The silane improved the adhesion, particularly in the presence of polar solvents such as water.
Polythiopolymercaptan polymers as disclosed in U.S. Pat. No. 2,466,963 are improved in adhesion by the addition of an adhesive additive compound having the structure HS--R--Si--(OR').sub.3. This composition and the process are claimed in U.S. Pat. No. 3,312,669, issued Apr. 4, 1967.
A moisture curable polysulfide composition is disclosed in U.S. Pat. No. 3,317,461, issued May 2, 1967. A polysulfide polymer is reacted with a vinyl silane to give a polysulfide endblocked with silyl groups which react upon exposure to moisture to provide crosslinking.
A curable, liquid polysulfide polymer based sealant is bonded to a substrate by priming the substrate with a primer containing at least one organic silane compound and at least one Friedel-Crafts compound, applying the curable composition to the primed substrate and curing the composition on the substrate. This process is claimed in U.S. Pat. No. 3,457,099, issued Jul. 22, 1969.
U.S. Pat. No. 3,476,826, issued Nov. 4, 1969, teaches polysulfide polymers having pendant organo-silane radicals containing hydrolyzable groups are effective as adhesion additives or primers for high rank polysulfide polymer compositions used as sealants or bonding agents on various substrates.
A process which uses a bis-trialkoxysilylorgano polysulfide compound as a primer for bonding polyurethane sealants and caulks to solid inorganic surfaces is taught in U.S. Pat. No. 4,015,044, issued Mar. 29, 1977.
U.S. Pat. No. 4,020,218, issued Apr. 26, 1977, discloses a process for enhancing the bonding of polysulfide sealant to solid inorganic substrates by providing an interface of a silane or its hydrolyzate having a bicyclopentenyl or mercaptonorbornyl containing radical.